1. Field of the Invention
The invention relates in general to an apparatus for automatically cleaning a mask. More particularly, this invention relates to apparatus for automatically cleaning a mask applied in an evaporation system.
2. Description of the Related Art
An evaporation system typically comprises a vacuum chamber for executing vacuum evaporation and a vacuum system to provide vacuum of the vacuum chamber. In the vacuum chamber, an evaporation source is disposed in a crucible made of high temperature conductive material. The crucible is connected with an external DC current source. When an appropriate amount of current flows to the crucible, the evaporation source is heated caused by the resistor of the crucible until reaching the melting point. The atoms evaporated from the evaporation source are then deposited as a thin film on the wafer which is disposed close by.
FIG. 1 shows a top view of an evaporation system. In FIG. 1, the evaporation system comprises a vacuum chamber 100 and a vacuum system 101. The vacuum system 101 is connected and external to the vacuum chamber 100. The vacuum chamber 100 comprises a crucible 102 and a mask positioning apparatus. The crucible 102 is located at a lower part inside the vacuum chamber 100 to carry the evaporation source 103. The mask positioning apparatus located at an upper part inside the vacuum chamber 100 comprises a wafer table 104 and a mask table 105. The wafer table 104 carries a wafer 106 for performing the thin film deposition. The mask table 105 carries a mask 107 to obtain a desired pattern of the deposition. The mask 107 is made of magnetic material. A magnet 108 is disposed on top of the vacuum chamber 100 to attract the mask 107 which can thus be adhered on the surface of the wafer 106. When an appropriate amount of current flowing to the crucible 102, the heat generated by resistance effect of the crucible 102 heat the evaporation source up to a melting point. The previously solid evaporation source 103 is thus evaporated to deposit a thin film on the wafer 106.
In the above conventional apparatus, as the step coverage of the thin film deposition is poor, hillocks are very likely formed on the wafer. After performing several times of evaporation processes, the mask to transfer the pattern on the wafer has been adhered with a lot of particles of evaporation source. The particles of evaporation source adhered on top surface or sidewall of the mask seriously affects the transferred pattern. Therefore, conventionally, the mask is a consumable part. After performing certain times of evaporation processes, the mask has to be renewed to maintain the quality of the transferred pattern. This greatly raises the fabrication cost and consumes a lot of process time and space for storing the masks.
The invention provides an apparatus for automatically cleaning a mask. The mask is fixed on the mask table and cleaned by an RF plasma in a vacuum chamber. Using the RF bias, the efficiency for evaporating the wafer can be enhanced.
The apparatus comprises an RF plasma generator, a wafer table and a mask table. Isolated from the grounded reaction chamber. The RF power source can thus be supplied to the wafer table and the mask table. During the evaporation process, an RF power is provided to cause a voltage drop of the bias, so that the mobility of the evaporation source toward the wafer is enhanced, so that the efficiency of evaporation is enhanced. After evaporation, the wafer is removed from the reaction chamber. The RF power source generates an RF plasma to bombard the mask, so that the particles of the evaporation source attached on the top surface and sidewall of the mask are removed. The mask can thus be kept on the mask table without being removed. As a result, the cost and time consumption can be saved.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.